Wood processing installations producing chips in pulp and paper mills, or separate chipping mills, must be able to receive and handle large quantities of logs of different lengths, varying from short, (2 to 3-meter) to treelength (12 to 18 meters) roundwood.
It is important for roundwood processing plants that all wood can be transported to the plant, including treelength stems. This is so that they can be barked and chipped in the condition in which they are received, which means that several extra timber processing steps (e.g. cross-cutting, transporting from one conveyor to another, etc.) are obviated in the installation. In addition, the following advantages emerge: the chip quality improves when long wood is being chipped; and wood losses and the amount of short billets become less. At the same time, the investment, labor and maintenance costs of the entire roundwood processing plant are reduced.
Although the debarking and chipping of long wood is economically the most advantageous, and qualitatively the best processing method, more extensive use of this method has been restricted by the low capacity of the long timber feeding methods and apparatus previously used and known in the art. It has been further restricted by the intermittent mode of operation, as well as the fact that such methods are only applicable in the case of long wood.
Since a procedure has been lacking which would enable the feeding of both long wood and short wood into the debarking drum using one and the same feeding means, it has been necessary heretofore either to cut up long tree stems on a circular saw deck, e.g. into two or more pieces, prior to feeding them into the debarking drum; or two separate feed lines serving the drum have been constructed, one for long wood and another for short wood.